Rising fuel costs and increasingly stringent environmental regulations such as carbon taxes are driving the development of aircraft propulsion systems with improved fuel efficiency. One aircraft propulsion system which is known to provide improved fuel efficiency and reduced carbon emissions is the open rotor propulsor. An open rotor propulsor is similar to a turbofan engine commonly used on commercial aircraft with the difference that an open rotor propulsor includes rotors that are external to the engine nacelle in contrast to a turbofan engine which includes one or more fans located inside the engine nacelle.
The rotors of an open rotor propulsor are larger in diameter than the nacelle of a turbofan engine and therefore require mounting at a higher location on the aircraft to provide ground clearance for the rotors. One solution to mounting open rotor propulsors at a high location is by supporting the propulsors on wings that are mounted to the top of the fuselage in a high-wing aircraft configuration. Unfortunately, mounting the wings on top of the fuselage requires a means for transferring the wing downward load down to the main landing gear which may be mounted toward the bottom of the fuselage. The wing downward load may include the structural mass of the wings and the mass of the open rotor propulsors, the fuel in the wing fuel tanks, and other systems that may be contained within or attached to the wings.
One approach to transferring the wing downward load into the main landing gear of a high-wing aircraft includes locally increasing the size of the fuselage frames in the area under the wings. For a fuselage having a cylindrical cross-sectional shape, the wing downward load must transfer from the top of the fuselage and down along the curved frames of the fuselage sidewalls and into the fuselage-mounted landing gear. Unfortunately, the curvature in the fuselage frames requires an increased height and/or thickness of the curved fuselage frames which results in the high-wing aircraft being generally heavier than a low-wing aircraft of approximately the same size.
Another approach to transferring the wing downward load into the main landing gear of a high-wing aircraft includes providing the fuselage in a square cross-sectional shape with straight sidewalls instead of a cylindrical shape with curved sidewalls. Straight sidewalls may transfer the vertical compression load of the wings into the main landing gear more efficiently than curved sidewalls. Unfortunately, a square fuselage may generate increased aerodynamic drag relative to a cylindrical fuselage. The increased aerodynamic drag of the square fuselage may reduce the aircraft fuel efficiency.
Yet another approach to transferring the wing downward load into the main landing gear of a high-wing aircraft includes adding a reinforcing bulkhead structure inside the aircraft cabin. Unfortunately, such a bulkhead structure displaces revenue-generating passenger seats and may require lengthening the fuselage to provide additional room for the displaced passenger seats. The lengthening of the fuselage may increase the total aircraft weight which may reduce the fuel efficiency of the aircraft.
As can be seen, there exists a need in the art for a system and method for transferring the wing downward load of a high-wing aircraft into a fuselage-mounted landing gear with a minimal increase in the weight of the aircraft. In addition, there exists a need in the art for a system and method for transferring the wing downward load of a high-wing aircraft into a fuselage-mounted landing gear which avoids the need to increase the length of the fuselage to accommodate a desired number of passenger seats. Ideally, the system and method may be integrated into a cylindrically-shaped fuselage to minimize aerodynamic drag.